ABSTRACT This application is a renewal for R01AA023522. The aims of the first cycle of funding were to evaluate the indirect effect of a Brief Motivational Intervention (BMI) for hazardous alcohol use among college students in a complete social network. We enrolled 90% (N = 1489) of the first-year class at one university, with follow-up rates of 98% and 96% at 5 and 12 months. All goals of the study were met, including establishing that heavy drinkers targeted for intervention because they are optimally connected to other heavy drinkers are responsive to a BMI (compared to Natural History Controls; NHC), and that group differences (BMI vs. NHC) are detectable among heavy drinkers who received no intervention, supporting the concept of an indirect intervention effect. Consistent with the social network literature that theorizes that changes in behavior among individuals can be transmitted to others, the purpose of this renewal study is to evaluate whether indirect intervention effects can be detected in older students at a time when friendships are established, most students are of legal drinking age, and most live off campus where alcohol-related risks are highest. In the later college years, emerging adults also progress through transitions in academic, vocational, and psychosocial areas. We will enroll a new class year (anticipated N = 1310), and use a two-group design in which heavy drinking clusters of students are randomly assigned to either BMI or NHC. A network node selection algorithm created in the current study will identify the most influential members of each cluster comprising 25% of heavy drinkers overall, N = 75 per group. In the BMI group these network members will receive a BMI in the spring of their junior year plus updated personalized feedback as a booster in the fall of their senior year, intended to address risks when a large percent of students move off campus; those selected in NHC will receive no contact. All participants in the network will be followed through their senior year and in the fall after graduation. Our aims are to (1) investigate the indirect effects of this intervention, that is, determine whether close friends of the heavy drinkers who receive the intervention benefit from it as well, (2) identify the social influence mechanisms through which the intervention recipients affect other heavy drinkers, (3) identify the network and relationship conditions under which the intervention is the most effective, and (4) determine whether the intervention, associated changes in alcohol use, and network factors influence developmental transitions critical for young adults. This renewal will capitalize on longitudinal assessment of the social network connections, associated peer interactions, and individual network members' substance use as they evolve from the mid-college to beyond graduation. Having data on alcohol involvement and network ties provides an unparalleled opportunity to identify how risk factors are transmitted through peer relationships as early adults mature through different times of risk, and determine whether those influences can be leveraged to reduce alcohol-related risk community wide.